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JEE Main 2023
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

If the truth value of the statement (P(R))((R)Q)(P \wedge(\sim R)) \rightarrow((\sim R) \wedge Q) is F, then the truth value of which of the following is F\mathrm{F} ?

Options

Solution

Key Concepts and Formulas

  • The implication ABA \rightarrow B is false if and only if AA is true and BB is false.
  • The conjunction ABA \wedge B is true if and only if both AA and BB are true.
  • The disjunction ABA \vee B is true if at least one of AA or BB is true.
  • The negation A\sim A is true if AA is false, and false if AA is true.

Step-by-Step Solution

Step 1: Analyze the given statement and its truth value.

We are given that (P(R))((R)Q)(P \wedge (\sim R)) \rightarrow ((\sim R) \wedge Q) is false. Using the fact that ABA \rightarrow B is false only when AA is true and BB is false, we can deduce: P(R) is trueP \wedge (\sim R) \text{ is true} (R)Q is false(\sim R) \wedge Q \text{ is false}

Step 2: Determine the truth values of P, Q, and R.

Since P(R)P \wedge (\sim R) is true, both PP and R\sim R must be true. Thus, P is true (T)P \text{ is true (T)} R is true (T)\sim R \text{ is true (T)} This implies that R is false (F)R \text{ is false (F)}

Now, consider (R)Q(\sim R) \wedge Q is false. Since we know that R\sim R is true, for the conjunction to be false, QQ must be false. Q is false (F)Q \text{ is false (F)}

So, we have P=TP = T, Q=FQ = F, and R=FR = F.

Step 3: Evaluate the truth values of the given options.

(A) PQRP \vee Q \rightarrow \sim R PQP \vee Q is TFT \vee F, which is TT. R\sim R is F\sim F, which is TT. Therefore, PQRP \vee Q \rightarrow \sim R is TTT \rightarrow T, which is TT.

(B) RQPR \vee Q \rightarrow \sim P RQR \vee Q is FFF \vee F, which is FF. P\sim P is T\sim T, which is FF. Therefore, RQPR \vee Q \rightarrow \sim P is FFF \rightarrow F, which is TT.

(C) (PQ)R\sim (P \vee Q) \rightarrow \sim R PQP \vee Q is TFT \vee F, which is TT. (PQ)\sim (P \vee Q) is T\sim T, which is FF. R\sim R is F\sim F, which is TT. Therefore, (PQ)R\sim (P \vee Q) \rightarrow \sim R is FTF \rightarrow T, which is TT.

(D) (RQ)P\sim (R \vee Q) \rightarrow \sim P RQR \vee Q is FFF \vee F, which is FF. (RQ)\sim (R \vee Q) is F\sim F, which is TT. P\sim P is T\sim T, which is FF. Therefore, (RQ)P\sim (R \vee Q) \rightarrow \sim P is TFT \rightarrow F, which is FF.

Step 4: Identify the option with a truth value of F.

From the evaluations above, we see that only option (D) has a truth value of F. However, the correct answer given is (A). There appears to be an error in the provided correct answer. We need to re-evaluate to find the error.

The original question states that we want to find the option that is FALSE.

Let's re-examine each option: (A) PQRP \vee Q \rightarrow \sim R P=T,Q=F,R=FP=T, Q=F, R=F (TF)(F)(T \vee F) \rightarrow (\sim F) TTT \rightarrow T which is TT.

(B) RQPR \vee Q \rightarrow \sim P FFTF \vee F \rightarrow \sim T FFF \rightarrow F which is TT.

(C) (PQ)R\sim (P \vee Q) \rightarrow \sim R (TF)F\sim (T \vee F) \rightarrow \sim F (T)T\sim (T) \rightarrow T FTF \rightarrow T which is TT.

(D) (RQ)P\sim (R \vee Q) \rightarrow \sim P (FF)T\sim (F \vee F) \rightarrow \sim T (F)F\sim (F) \rightarrow F TFT \rightarrow F which is FF.

So (D) is the only option that is false. However, the correct answer says (A). There must be an error in the problem or the provided correct answer. Let's double-check the initial assignments of T/F to P, Q, and R.

(P(R))((R)Q)(P \wedge (\sim R)) \rightarrow ((\sim R) \wedge Q) is False. So P(R)P \wedge (\sim R) is True and (R)Q(\sim R) \wedge Q is False. PP is True and R\sim R is True, which means RR is False. Since R\sim R is True, then for (R)Q(\sim R) \wedge Q to be False, QQ must be False. So P=TP=T, Q=FQ=F, R=FR=F.

Let's check option A again. PQRP \vee Q \rightarrow \sim R TFFT \vee F \rightarrow \sim F TTT \rightarrow T which is TT. This is NOT False.

Since we have re-verified all the steps, there is an error in the given correct answer. The correct answer should be (D).

Common Mistakes & Tips

  • Carefully analyze the truth table for implications and conjunctions. A single mistake here will propagate through the entire solution.
  • Remember that ABA \rightarrow B is only false when AA is true and BB is false. In all other cases, it is true.
  • Double-check your truth value assignments for P, Q, and R.

Summary

We are given that (P(R))((R)Q)(P \wedge (\sim R)) \rightarrow ((\sim R) \wedge Q) is false. From this, we deduced that PP is true, QQ is false, and RR is false. Substituting these values into the given options, we found that option (D), (RQ)P\sim (R \vee Q) \rightarrow \sim P, is the only one with a truth value of F. The originally provided answer was incorrect.

Final Answer

The final answer is \boxed{D}, which corresponds to option (D).

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